1. Field of the Invention
The present invention relates to methods and apparatus for allocating acknowledgement channels in a communication network.
2. Description of the Related Art
This application, pursuant to 37 C.F.R. §1.57, incorporates by reference the following publications:
[1] R1-080135, “Implicit assignment of PHICH”, Panasonic;
[2] R1-080301, “PHICH and mapping to PHICH groups”, Nokia, Nokia Siemens Networks; and
[3] R1-080668, “PHICH linking to downlink CCE”, Samsung, Panasonic.
Telecommunication enables transmission of data over a distance for the purpose of communication between a transmitter and a receiver. The data is usually carried by radio waves and is transmitted using a limited transmission resource. That is, radio waves are transmitted over a period of time using a limited frequency range.
In a contemporary communication system, the information to be transmitted are first encoded and then modulated to generate multiple modulation symbols. The symbols are subsequently mapped into transmission resource. Usually, the transmission resource available for data transmission is segmented into a plurality of equal duration time and frequency slots, so called resource elements. A single resource element or multiple resource elements may be allocated for transmitting the data. When data is transmitted, a control signal may accompany the data to carry information regarding the allocation of the resource elements for the current data transmission. Therefore, when a receiver receives the data and the control signal, the receiver may derive the information regarding resource allocation used for data transmission from the control signal and decodes the received data using the derived information.
In Third (3rd) Generation Partnership Project Long Term Evolution (3GPP LTE) systems, certain resource elements are allocated for control signal transmission. Therefore, the data symbols may be mapped into the resource elements that are not allocated for control signal transmission. Each data transmission carries information bits of one or multiple transport blocks. When a transport block is larger than the largest code block size, the information bits in a transport block may be segmented into multiple code blocks. The process of dividing the information bits in a transport block into multiple code blocks is called code block segmentation. Due to the limited selection of code block sizes and the attempt to maximize packing efficiency during the code block segmentation, the multiple code blocks of a transport block may have different sizes. Each code block will be encoded, interleaved, rate matched, and modulated. Therefore, the data symbols for a transmission may consist of modulation symbols of multiple code blocks.
Currently, a few methods were proposed to allocate the Physical Hybrid Automatic Repeat-reQuest (HARQ) Indicator Channel (PHICH). PHICH is also known as downlink acknowledgement channels that are used by base station (Node B) to acknowledge (ACK) or negatively acknowledge (NAK) uplink transmissions by user equipments (UEs).
Methods to link the PHICH allocation to the Control Channel Elements (CCE) of Physical Downlink Control Channel (PDCCH) were proposed in Reference [1] and Reference [3]. These methods allow efficient PHICH allocation, but suffer from the complexity of handling CCE scheduling in packet data control channel (PDCCH).
Methods to link the PHICH allocation to uplink Physical Resource Blocks (PRB) were proposed in Reference [2]. These methods allow simple PHICH allocation and CCE scheduling, but the resources allocated for PHICH are often inefficiently utilized.